1. Field of the Invention
The present invention relates to a travelling worktable apparatus (a sample travelling worktable apparatus or a sample stage apparatus) for semiconductor manufacturing apparatuses, semiconductor inspecting apparatuses, and working tools to achieve fine machining with high precision, and in particular, to improvement of measurement errors in measurement of a position of a sample.
2. Description of the Related Art
In general, in semiconductor manufacturing apparatuses and/or semiconductor inspecting apparatuses, a travelling stage apparatus (travelling worktable apparatus) to transport a sample such as a wafer must have a positioning function with high precision. Therefore, a laser for high-precision measurement is usually employed to detect a sample position. In such a configuration, a position of a mirror placed on a sample table is measured by a laser to control the sample position. In the detection of the sample position according to values measured by a laser, variation in distance between the mirror (bar mirror) and the sample has been heretofore neglected. However, in an apparatus which requires higher precision in the positioning of a sample, the distance between the bar mirror and the sample varies by deformation of the table caused by a guide apparatus, for example, deviation in precision of rollers used in the guide apparatus and precision in attachment of the guide apparatus. It is consequently difficult to control the sample position with high precision.
Referring to FIGS. 1 and 2, description will be given of the problem for easy understanding of the gist of the problem.
First, description will be given of a configuration of a general travelling table apparatus of FIG. 1 and a measuring method of the apparatus.
The configuration of FIG. 1 includes a top table 1 which can travel in an x-axis direction and in a y-axis direction, an X bar mirror 5 for x-directional measurement, and a Y bar mirror 6 for y-directional measurement. A sample 30 is placed on the top table 1. It is necessary to keep the sample 30 at the position when the top table 1 is moved. Therefore, the sample is adsorbed onto the top table 1 using vacuum or electrostatic force or is mechanically fixed thereon. First, the x-directional measurement will be described. Laser emitted from a laser head 10 is split by a beam splitter 9. Resultant light proceeds via an interferometer 7 in a direction vertical to the X bar mirror 5. Reflected light from the mirror 5 again passes through the interferometer 7 (the light again reflects on the mirror 5 in a double-path system). There is obtained interference light. The light is then received by a receiver 8. The receiver 8 accordingly produces a signal indicating a position of the mirror 5. Also in the y-axis direction, the distance between the interferometer 7 and the Y bar mirror 6 can be detected in a similar way. If the distance between the sample and each of the bar mirrors is kept unchanged, the sample position can be controlled with high precision according to variation in the distance of each bar mirror.
However, when the top table 1 is deformed as shown in FIG. 2, distance between a center of the sample 30 on the top table 1 and the mirror for x-directional measurement increases by xcex94X relative to original distance X therebetween. An error of xcex94X appears in a measured value of distance, and hence the sample positioning precision is lowered.
JP-A-1-274936 describes a prior art example of a travelling stage (X-Y stage). In the configuration of the travelling stage, springs are inserted respectively in a pressurized section and a fixing section of a guide rail so that the guide rail frees deformation of the table caused in association with the precision of the guide apparatus described above or by variation in temperature and a thermal expansion coefficient.
FIG. 11 shows the freeing structure of the guide rail in the prior art example in a schematic diagram.
In the configuration shown in FIG. 11, a coned disc spring 85 is disposed on a support pin 83 of a guide rail 82 on pressurized side, the guide rail being attached onto a travelling table 80. Compressive force of the spring 85 brings the guide rail 82 into tight contact with the travelling table 80. This allows a degree of freedom for the guide rail 82 with respect to variation in pressure beforehand applied on the pressurized side. Also in the pressurized section, a compression spring 87 is arranged for a pressure pin 89 to keep the pressure of the guide apparatus at a predetermined level. This also contributes to suppress deformation of the table 80.
In the configuration of the prior art example, the spring 85 is used to bring the guide rail 82 into tight contact with the travelling table 80. The guide rail 82 on the pressurized side has a degree of freedom also in other than the pressurized direction.
In other words, movement of the table 80 in a direction vertical to an upper surface of the table 80 depends on compressive force of the spring 85. Therefore, when there appears acceleration due to shock or vibration in the vertical direction, the upper surface of the table 80 easily becomes unstable. To overcome this difficulty, if it is desired to increase rigidity of the table 80 in the vertical direction, the spring 85 must have a larger spring modulus. However, to guarantee the original purpose, namely, the smooth shift toward the pressurized direction, frictional force on the attaching surface must be minimized.
For this purpose, it can be considered a method to reduce roughness of the attaching surface, namely, to smooth the surface like a mirror surface. However, in consideration of the overall travelling table, since rigidity of the table in the travelling direction is as low as that in the pressurized direction, the structure becomes weak with respect to self-excited vibration and/or external disturbance.
It is therefore an object of the present invention to provide a travelling worktable apparatus in which deformation of the guide apparatus is reduced to a low level while keeping rigidity of the guide apparatus such that the distance between the mirror and a sample placed on the upper surface of the table can be kept fixed.
In accordance with the present invention, there is provided a travelling worktable apparatus, comprising a fixed base, an intermediate table mounted on said fixed base with a first guide disposed therebetween, said intermediate table being capable of achieving a reciprocating motion, a top table mounted on said intermediate table with a second guide disposed therebetween, said top table being capable of achieving a reciprocating motion in a direction which intersects a direction of the reciprocating motion of said intermediate table; and a measuring mirror disposed on said top table. The top table comprises a travelling table for holding said second guide, a sample table disposed on said travelling table for mounting a sample thereon, a pin for restricting said travelling table and said sample table, said pin being more easily deformed than said travelling table and said sample table; and an elastic body disposed between said travelling table and said sample table.